To meet the requirements for faster performance, the characteristic dimensions of features of integrated circuit devices have continued to be decreased. Manufacturing of devices with smaller feature sizes introduces new challenges in many of the processes conventionally used in semiconductor fabrication. One of the most important of these fabrication processes is photolithography.
It has long been recognized that linewidth variations in patterns produced by photolithography can result from optical interference from light reflecting off an underlying layer on a semiconductor wafer. Variations in photoresist thickness due to the topography of the underlying layer also induce linewidth variations. Anti-reflective coatings (ARC) applied under a photoresist layer have been used to prevent interference from reflection of the irradiating beam. In addition, anti-reflective coatings partially planarize the wafer topography, helping to improve linewidth variation over steps because the photoresist thickness is more uniform.
Organic polymer films, particularly those that absorb at the i-line (365 nm) and g-line (436 nm) wavelengths conventionally used to expose photoresists, and at the recently used 248 nm wavelength, have been employed as anti-reflective coatings. However, the fact that the organic ARC's share many chemical properties with the organic photoresists can limit usable process sequences. Furthermore organic ARC's may intermix with photoresist layers. One solution to avoid intermixing, is to introduce thermosetting binders as additional components of organic ARC's, as described, for example in U.S. Pat. No. 5,693,691 to Flaim et al. Dyes may also be incorporated in organic ARC's, as well as, optionally, additional additives such as wetting agents, adhesions promoters, preservatives, and plasticizers, as described in U.S. Pat. No. 4,910,122 to Arnold et al.
Silicon oxynitride is another material that has been used as an anti-reflective coating. However, silicon oxynitride works as an ARC by a destructive interference process rather than by absorption, which means that very tight control of the oxynitride thickness is necessary and that the material may not work well as an ARC over highly variable topography. Furthermore silicon oxynitride is typically deposited by chemical vapor deposition, while photoresist layers are typically applied using a spin-coater. The additional chemical vapor deposition process can add to processing complexity.
Yet another class of materials that can be used as an antireflective layer is spin-on-glass (SOG) compositions containing a dye. Yau et al., U.S. Pat. No. 4,587,138, disclose a dye such as basic yellow #11 mixed with a spin-on-glass in an amount approximately 1% by weight. Allman et al. U.S. Pat. No. 5,100,503 disclose a cross-linked polyorganosiloxane containing an inorganic dye such as TiO2, Cr2O7, MoO4, MnO4, or ScO4, and an adhesion promoter. Allman additionally teaches that the spin-on-glass compositions also serve as a planarizing layer. However, the spin-on-glass, dye combinations that have been disclosed to date are not optimal for exposure to the deep ultraviolet, particularly 248 and 193 nm, light sources that are coming into use to produce devices with small feature sizes. Furthermore, not all dyes can be readily incorporated into an arbitrary spin-on-glass composition.
U.S. Pat. No. 5,328,975 teaches titanium oxide/silicon oxide coating compositions having UV radiation absorbing properties. U.S. Pat. No. 5,520,855 teaches a composition of metal alkoxide, pigment, alcohol, and dispersant having light absorbing properties. U.S. Pat. No. 5,731,091 teaches a composition of hydrolyzable silane, organosilane, and temperature-stable dyes. However, these patents do not teach or suggest the present compositions having an unique absorbing compound.
Honeywell Accuglass® 108 product comprises methylphenylsiloxane and phenyl tetraethoxysilane. Unfortunately, the Honeywell Accuglass® 108 product etches non-uniformly and has an extinction coefficient k (measured at 193 nm wavelength) of 0.106 to 0.094 and an extinction coefficient k (measured at 248 nm wavelength) of zero and thus, does not strongly absorb light as is desired for spin-on-glass anti-reflective coating material.
Honeywell Accuglass 204® product comprises phenylsiloxane and phenyl tetraethoxysilane. Unfortunately, the Honeywell Accuglass 204® product etches non-uniformly and has an extinction coefficient k (measured at 193 nm wavelength) of 0.268-0.236 and an extinction coefficient k (measured at 248 nm wavelength) of zero and thus, does not strongly absorb light as is desired for spin-on-glass anti-reflective coating material.
Honeywell Accuglass ® 720 material comprises methylphenylsilsequioxane of the general formula (R-0-1.0)(SiO1.5-2.0)m and phenyl tetraethoxysilane and has an extinction coefficient k (measured at 193 nm wavelength) of 0.485 to 0.404 but unfortunately has an extinction coefficient k (measured at 248 nm wavelength) of zero and an inadequate etch rate of zero Angstroms/minutes in a hydrofluoric acid bath.
What is needed is an absorbing spin-on-glass anti-reflective coating material that absorbs strongly and uniformly in the deep ultraviolet spectral region. It would be desirable for the ARC layer to be impervious to photoresist developers. It would also be desirable to provide a method to incorporate a range of absorbing compounds into a variety of SOG materials while retaining the desirable properties of the original spin-on-glass materials.